There are many situations in which there is a need to determine the time and/or date of a writing. Possibly the most obvious example to anyone reading this document is the need to prove the date of a writing to show conception of an invention on or before the effective date of a prior art document or event. For example, in the U.S. first-to-invent system, a first inventor of an invention who files a U.S. patent application after a second inventor files a U.S. patent application on the same subject matter may be able to “win” the patent rights in a priority contest if the first inventor can show prior conception and diligence from before the second inventor's conception to the first inventor's U.S. filing date. One way to show prior conception is, e.g., to provide detailed laboratory notes that disclose the invention. Typically, to convince a jury, the notes must be dated and witnessed.
A problem with this method is multifaceted. First, an independent inventor may be unfamiliar with U.S. law and may have insufficient corroborating evidence to prove the asserted date of conception. Second, if the witness is biased (such as if the witness works for the same company as the inventor), her testimony may be insufficient to corroborate the written lab notes. Third, if the witness is not one of skill in the art, the witness may not be able to convince a jury that she knew the inventor possessed the invention on the asserted conception date. If, in addition to any witness testimony, the inventor can physically prove a date that the ink was placed on the lab note paper, this additional evidence may be sufficient to convince a jury of the asserted conception date. Thus, there has been a need to determine the age of ink. Of course, this need exists in other fields besides inventorship, conception, and patents. For example, a person may want to prove that he signed a legal document on a particular date, or may want to prove that he wrote certain entries in a legal document on different dates. Such a need often arises in expensive litigation, such as insurance litigation. A claimant, who may have been accused of insurance fraud by making several dated entries (dated on different days) on the same day. The claimant may be able to counter this accusation by determining the age of the ink on each of the entries. One skilled in the art will recognize that there is a wide host of situations in which one needs to determine the age of ink deposited on a writing surface (such as paper).
Presently, ink dating analysis is based on the observation that typical ball-point ink does not fully dry for up to five years. Because wet ink and dry ink dissolve in a solvent at different rates, the approximate age of ink on a writing surface may be determined by dissolving a known quantity of the drying ink in a solvent and timing the rate of dissolution; the faster the dissolution, the more recently the ink was applied to the writing surface. There are a host of problems with this method. First, because currently available inks vary widely in their properties, such as chemical content, viscosity, and vapor pressure, the age of the ink determined by this method is very approximate, and cannot yield the kind of accurate dating required in some litigation. Second, the method is easy to fool. A defrauder may attempt to make a written ink appear much older than it actually is simply by heating or cooking the document. Applying heat to ink increases its vapor pressure and the rate at which it dries. Alternatively or in addition, the defrauder may place the document in a vacuum chamber, where the ink will naturally dry more quickly than in the atmosphere.
One attempt to solve the first problem above (the inherent uncertainties in current ink aging analyses) is disclosed in U.S. Pat. Nos. 5,600,443 and 5,759,246 to Frey et al. Frey discloses a method and ink composition of two possible mechanisms. The first mechanism relates to detecting color shifts of pH sensitive compounds in the ink as the result of the evaporation of certain acidic or basic compounds thereof. The second mechanism relates to the oxidation of compounds in the ink by reaction with oxygen in the air. Frey does not solve the second problem posed above (the ease of defrauding). For example, in the first mechanism, the evaporation of the certain acidic or basic compounds in the ink can be artificially accelerated by a defrauder by either heating the inked document or placing the inked document in a vacuum chamber. In the second mechanism, the oxidation of the compounds can be artificially accelerated by a defrauder by either heating the inked document or placing the inked document in a pressure chamber in which the oxygen density is higher than in the atmosphere. For example, because the sea-level atmosphere has a pressure of about 1 atm and contains about 20% oxygen, the oxidation of the compounds may be artificially accelerated by placing the inked document in a pressure chamber such that the pressure chamber contains a pressure higher than atmospheric, an oxygen content of greater than 20%, or both. Thus, it is relatively easy to make the ink of Frey appear that it was placed on the document in question on a date much earlier than it actually was.